Research On SLM-based Maskless Lithography

In recent years, optical maskless lithography technique based on spatial light modulator(SLM) has been attracted wide attentions. SLM is adopted as pattern generator in maskless lithography because of its convenience, programmable control and parallel print. SLM-based maskless lithography technique plays a very important role in the fabrication of high-quality mask and micro optical elements(MOE), especially for low-volume runs, and further provides potential application in high-resolution integrated circuits(IC) fabrication. Now it is an important target to develop SLM-based maskless lithography technique in lithographic community. To meet the continuously increasing requirement of nanofabrication and promote the rapid development of microelectronic and MOEMS techniques in China, and aiming at developing the imaging theory of SLM lithography and building SLM-based maskless lithography system, we made a comprehensive and systemic study on MEMS mirror's optical features, the imaging quality of SLM-based maskless lithography and its applications in this dissertation.1. The partial coherent imaging theory used in lithographic system with the exposure and development theories in resist was academically summarized, and the peculiarities of several SLMs for lithography were studied in detail. Following the build of their mathematical models, the optical characteristics of tilting mirrors, piston mirrors and digital micro device(DMD) were analyzed, and then their differences in imaging effect were compared to obtain their imaging features, and further the theoretic model and emulation algorithm suitable for depicting the imaging process of SLM-based maskless lithography were built, and finally a program was developed to simulate SLM-based optical lithography process, which provide the theoretic base for analyzing the imaging of SLM-based maskless lithography, choosing the parameters of MEMS mirrors as digital mask and designing the optical path in SLM-based maskless lithography system.2. The conditions of SLM-based maskless lithography for the fabrication of IC were analyzed, and the methods for the improvement of lithographic resolution were explored. The study results show that there are some advantages in SLM-based maskless lithography such as basic CD adjustment, edge positioning with grayscaling, arbitrarily placing minimum features with good imaging quality, and so on. According to the shortcoming of the sensitivity to defocus, we presented to use different mirrors' arrangement tricks to correct it. We also studied the optical proximity effects in SLM-based maskless lithography and develop Newton-Raphson algorithm for adjusting the deflection quality of MEMS mirrors to improve the imaging quality.3. DMD-based gray-tone lithography technique was discussed, and the theoretical and experimental studies of the fabrication of MOE with the technique were performed. We explored the exposure methods for fabricating MOE and the methods for improving MOE fabrication quality in detail which involves removing grid effect, deducing data delivery and correcting edge aberration, etc. Due to the data delivery technique of pulse width modulation easily bringing surface aberrations in fabricating MOE, we presented two methods to solve it, namely, to adjust the coherence of illumination source and optimize the mask design. Through the modification of the imaging system and the process parameters, we fabricated some MOEs with good profile, which gives out a new path to fabricate microstructure elements.4. Now nanofabrication and surface plasmon polariton(SPP) techniques are being explored, and meanwhile it is our pursuit purpose to develop maskless nanofabrication technique beyond the diffraction limit. We try to apply SPP to maskless lithography in the lattermost chapter. Through the in-depth analysis of the physical forming mechanism and the characteristics of SPP, we presented to use wide beam illumination with ATR coupling mode to realize large-area interference lithography, and further presented to use SPP resonance transmission in thick metal film to fabricate quasi-periodic, non-periodic and arbitrary nanostructures, which is expected to be a new nanofabrication tool when combining with SLM maskless lithographic technique.